[46.13] GHRS Observations of the M-giant $\gamma $ Cru

K. Carpenter (NASA-GSFC), R. Robinson (CSC), S. Gessner (USRA)

The Goddard High Resolution Spectrograph (GHRS) on the Hubble Space Telescope
has been used to obtain medium (R=20,000) and high (R=85,000) resolution UV
spectra of chromospheric emission features for the M3.4 III star $\gamma$~Cru.
Large Science Aperture (LSA), medium resolution spectra were obtained to survey
the 1980 - 2200 \AA\ region with good signal-to-noise. Small Science Aperture
(SSA) G270M and Echelle-B spectra of selected longer wavelength regions were
obtained to allow the measurement of velocity flows and turbulence for a
variety of ions, including C~II, Fe~II, Co~II, Si~I/II, Ni~II, Mn~II, and
Mg~II. Gaussian fits to the optically thin C~II (UV~0.01) intercombination
lines and fluorescently-excited lines of Co~II, Ni~II, Fe~II, and Si~I
indicate average turbulent velocities (Doppler FWHM) of 30.2 and 28.6 km/s,
respectively. For comparison, the C~II turbulent velocity previously measured
for the K5 giant $\alpha $ Tau is $\approx$~24 km/s. The measured
radial velocities of the fluorescent lines average 21.5 km/s, which places them
basically at rest relative to the radial velocity of the star (21~km/s), while
the C~II lines average 23.1 km/s, a modest inflow of a couple of km/s. A
subset of the collisionally-excited Fe~II emission lines show an average radial
velocity of 22.6 km/s, also a very modest inflow, at best. The stronger Fe~II
lines exhibit a more complex profile which consists of a broad emission line
with an $\approx$~40 km/s FWHM, on which are superposed two absorption
components. The stronger component appears at relatively low radial velocity
(in the 7 - 15 km/s range) in each line, with a mean value over the sample of
$\approx$~10.5 km/s, while the weaker component appears at relatively high
radial velocity in each line (in the range from 25 to 34 km/s), with a mean
value of $\approx$~31.3 km/s. The first represents an outflow of about 10 km/s,
while the second an inflow of about 10 km/s. The Mg~II h and k emission lines
also show the dual-absorption structure seen in the Fe~II lines. However, both
the emission and absorption components in the k-line are red-shifted by 7 to
9.5 km/s, relative to their equivalent components in the h-line.